1. Field of the Invention
The invention relates in general to a wireless communication receiving circuit using frequency shift key (FSK), and more particular, to a signal frequency splitter obtaining a plurality of local carrier signals used in frequency shift key by a frequency mixture manner and a frequency shift key decoding apparatus using the signal frequency splitter.
2. Related Art of the Invention
The conventional computer system is composed of a display, a computer host and some electrically connected peripherals. Peripherals operated by the user are restricted by the range of the computer desk. The fast development of the computer industry, plus the broad application of the Internet, has connected computers to the daily lives of many people. In addition, competition and the demand for light, thin, short and small exterior features continuously demands for the enhancement of operation speed and convenience in the industry. The industry relating to the peripherals of the computer system has developed some wireless input apparatus such as a wireless mouse, wireless keyboard, and has even convened USB interfaced peripherals into wireless peripherals. Such apparatus provides operation convenience for the user, by reducing the problems of wire connection.
If the peripherals are all converted into wireless equipment such as a wireless mouse and wireless keyboard, each piece of the equipment requires an individual wireless transmitter and an individual receiver. The extra cost is significant. Further, interference for signal transmission is inevitable. In addition, too many wireless peripherals may be problematic for integrating home appliances with the computer. Therefore, using the frequency shift key communication technique to integrate all the wireless transceivers into a single entity can offer a good resolution.
It is known in the art that the frequency shift key communication technique uses radio frequency signals with different frequencies as carriers to emit for different data. The data for different peripherals can thus be transmitted to the receiver via wireless communication simultaneously. In contrast, the receiver has to generate a plurality of corresponding local carrier signals for data signal separation and reduction. FIG. 2 shows a conventional multi-function wireless receiver supporting multiple peripherals. Referring to FIG. 2, the receiver has an oscillation crystal 134 and vibration initiator (not shown) to provide system frequency signal Fs required for operation of microprocessor 136. The system frequency signal Fs is supplied to a plurality of frequency synthesizers 251, 252, . . . , 25n simultaneously. According to the system frequency signal Fs, the frequency synthesizers 251, 252, . . . , 25n generate a plurality of local carrier signals Fb1, Fb2, Fbn. When the wireless receiver is operated, the low noise amplifier 124 amplifies the signal received by the antenna 122 to obtain a radio frequency signal. The mixers M21, M22 to M2n mix the radio frequency signal with the local carrier signals Fb1, Fb2 to Fbn. After being filtered by the intermediate-frequency filter 128, a plurality of intermediate-frequency signals corresponding to the data transmitted from different peripherals are obtained. As shown in FIG. 2, the frequencies of the local carrier signals Fb1, Fb2 to Fbn in the multi-function wireless receiver that supports multiple peripherals can be randomly changed. However, the n frequency synthesizers and one oscillation crystal required for generating local carrier signals Fb1, Fb2 to Fbn are very costly.
FIG. 3 shows another multi-function wireless receiver that supports multiple peripherals. In FIG. 3, in addition to the oscillation crystal 134 and the vibration initiator (not shown) required to generate the system frequency signal Fs required for the operation of the microprocessor 136, the receiver further uses a plurality of different oscillators 351, 352, . . . , 35n and vibration initiators (not shown) to generate local carrier signals Fb1, Fb2 to Fbn used for data signal separation and frequency reduction. In the conventional receiver, (n+1) oscillation crystals and vibration initiators are used. The more peripherals to be supported, the more oscillation crystals and vibration initiators are required. Consequently, the cost is increased. Being restricted by the fixed radio frequency baseband signal, the frequency cannot be changed.
According to the above, the multi-function wireless receiver supporting multiple peripherals has the following drawbacks.
1. If the signal frequency splitter uses a plurality of frequency synthesizers to generate a plurality of local carrier signals, though the frequency of the local carrier signals can be randomly changed, the system is very costly.
2. If the signal frequency splitter uses a plurality of oscillation crystals and vibration initiators to generate a plurality of local carrier signals, the cost is high, the frequency of the local carrier signals cannot be changed, and the system flexibility is poor.
3. In the above two approaches, the restriction in cost and circuit design causes the frequency shift key decoding apparatus formed by integrating a signal frequency separation apparatus and the demodulator into a single chip to be difficult.